Heat the oil in a large stove-top pot.Throw in the black mustard seeds and cook until they just start popping.Throw in the chillies and cook for 2-3 minutes until pungent.Add the star anise, cardamom, cloves, cinnamon, turmeric and both masalas. Stir vigorously and cook for 2-3 minutes. Add a little more olive oil to moisten if necessary.Add the garlic and chopped onion, stir into the mixture and cook for 3-4 minutes until softened and beginning to brown.Add the chicken pieces, stir in well and cook for 3-4 minutes or so.Add the carrots (and potatoes if you wish) and enough water to just cover all ingredients. Stir well.Cook slowly over a very low heat – or transfer to a low heat in the oven – for about an hour. Check occasionally, adding more water as necessary to make the curry have as much or as little gravy as you wish.

The longer you cook this curry, and the older the pot you cook it in, the better it will taste. Works pretty well in a slow-cooker too, but you have to cook all the spices manually first (method up as far as adding the chicken) as laid out above, then you can leave to simmer in the slow cooker if you wish.